This study concerns panic disorder with or without agoraphobia, psychiatric conditions which are associated with intense discomfort and significant social incapacitation, and which affect 10 million Americans. The study is based on the results of a pilot investigation, which suggested that there was an association between panic disorder and abnormal findings on vestibular and audiological tests. We are proposing a controlled evaluation of otoneurological function in panic disorder in a case-control design. We will contrast the prevalence of abnormal audiovestibular findings across five different diagnostic groups: (1) Panic disorder without agoraphobia; (2) Panic disorder with agoraphobia; (3) Generalized Anxiety disorder; (4) Dysthymic disorder; and (5) Normals (no psychiatric disorder). After initial diagnostic evaluations, 46 subjects of each group, or a total of 230 subjects, will receive a battery of clinical audiological and vestibular tests. The vestibular tests include: moving platform posturography, rotational, positional and caloric tests. The audiological test include: tympanometry, pure tone and speech discrimination audiograms, unilateral and crossed acoustic reflexes and auditory brain stem evoked potentials. The evaluators of the audiological and vestibular tests will be blind as to the diagnosis of the subjects. The results of these tests will be examined with respect to prevalence of clinically abnormal findings. Furthermore, parametric analysis of unprocessed data will test for systematic differences between diagnostic groups over the entire normal and abnormal range. The relationship between panic phenomenology and vestibular anomalies will be examined. The effect of hyperventilation on vestibular function will be studied. The results of the study will have clinical implications for the treatment and assessment of panic disorder.